(C++) virtual

Keyword helping you designing derived classes. A virtual function in the base class hints that this can be overloaded in the derived class. Or that it has to be defined in the derived class.

The C++ keyword virtual is not supported in C.

Example

include <iostream>


class MyBaseClass
{
  public:
  MyBaseClass() { ; }
  virtual void sayHello() const = 0; //MUST be defined in derived class
};
class MyDerivedClass : public MyBaseClass
{
  public:
  MyDerivedClass() { ; }
  void sayHello() const { std::cout << "Hello world" << std::endl; }
};
int main()
{
  //MyBaseClass myBaseClass; //Will give error below
  MyDerivedClass myDerivedClass;
  myDerivedClass.sayHello();
}

The line with the error gives the following error when uncommenting it:

cannot declare variable `myBaseClass' to be of type `MyBaseClass' 
because the following virtual functions are abstract: 
virtual void MyBaseClass::sayHello() const

Topic links

'virtual' links

last edited (November 18, 2006) by bilderbikkel, Number of views: 3386, Current Rev: 6 (Diff)

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